GitLab

* add sagpool example for pytorch backend

* polish sagpool example for pytorch backend

* [Example] SAGPool: use std variance

* [Example] SAGPool: change to std

* add sagpool example to index page

* add graph property prediction tag to sagpool

* [Example] add graph classification example HGP-SL

* [Example] fix sagpool

* fix bug

* [Example] change tab to space in README of hgp-sl

* remove redundant files

* remote redundant network

* [Example]: change link from code to doc in HGP-SL

* [Example] in HGP-SL, change to meaningful name

* [Example] Fix path mistake for 'hardgat'
Co-authored-by: zhangtianqi <tianqizh@amazon.com>